linux-kernel - Re: [PATCH v2 08/12] sched/wait: Drop WQ_FLAG_EXCLUSIVE from add_wait_queue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aC0AEJX0FIMl9lDy@google.com>
Date: Tue, 20 May 2025 15:20:00 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Ingo Molnar <mingo@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, K Prateek Nayak <kprateek.nayak@....com>, 
	David Matlack <dmatlack@...gle.com>, Juergen Gross <jgross@...e.com>, 
	Stefano Stabellini <sstabellini@...nel.org>, 
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH v2 08/12] sched/wait: Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority()

On Tue, May 20, 2025, Peter Zijlstra wrote:
> On Mon, May 19, 2025 at 11:55:10AM -0700, Sean Christopherson wrote:
> > Drop the setting of WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() to
> > differentiate it from add_wait_queue_priority_exclusive().  The one and
> > only user add_wait_queue_priority(), Xen privcmd's irqfd_wakeup(),
> > unconditionally returns '0', i.e. doesn't actually operate in exclusive
> > mode.
> 
> I find:
> 
> drivers/hv/mshv_eventfd.c:      add_wait_queue_priority(wqh, &irqfd->irqfd_wait);
> drivers/xen/privcmd.c:  add_wait_queue_priority(wqh, &kirqfd->wait);
> 
> I mean, it might still be true and all, but hyperv seems to also use
> this now.

Oh FFS, another "heavily inspired by KVM".  I should have bribed someone to take
this series when I had the chance.  *sigh*

Unfortunately, the Hyper-V code does actually operate in exclusive mode.  Unless
you have a better idea, I'll tweak the series to:

  1. Drop WQ_FLAG_EXCLUSIVE from add_wait_queue_priority() and have the callers
     explicitly set the flag, 
  2. Add a patch to drop WQ_FLAG_EXCLUSIVE from Xen privcmd entirely.
  3. Introduce add_wait_queue_priority_exclusive() and switch KVM to use it.

That has an added bonus of introducing the Xen change in a dedicated patch, i.e.
is probably a sequence anyways.

Alternatively, I could rewrite the Hyper-V code a la the KVM changes, but I'm not
feeling very charitable at the moment (the complete lack of documentation for
their ioctl doesn't help).